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From pizzly bears to strange fish, here’s why hybrid animal sightings are on the rise

<i>Troy Maben/AP via CNN Newsource</i><br/>A mounted polar bear-grizzly bear hybrid in Glenns Ferry
Troy Maben/AP via CNN Newsource
A mounted polar bear-grizzly bear hybrid in Glenns Ferry

By Ella Nilsen, CNN

(CNN) — The bear scientists shot in the Canadian arctic in 2016 was a biological mystery. It looked like a grizzly bear, complete with long claws and a prominent snout, but most of its fur was white.

Call it a pizzly or maybe a grolar bear. Either way, scientists determined the animal was the rare offspring of a polar bear that mated with a grizzly, and as the Arctic melts and polar bears increasingly move on land, sightings of these hybrids are on the rise.

Pizzly bears aren’t being born en masse, said Charlotte Lindqvist, a biology professor at the University of Buffalo whose lab focuses on evolutionary genetics. The accounts of the bears are mostly anecdotal, and it’s unclear how widespread the phenomenon is.

For instance, eight of the bear hybrids were found to be the children of a particular female polar bear with a seeming proclivity for male grizzlies.

But as global temperature rises and Arctic ice melts, polar bears will have more chances to encounter – and mate with – other bear species.

“This might just be the beginning,” Lindqvist told CNN. “The pressure is on, and we can clearly see in certain areas polar bears are spending more time on land as the sea ice is disappearing. Brown and black bears are encroaching on more Arctic habitat. And I think that’s just going to expand.”

Gene-swapping among bears and other animals and plants (and humans) has been happening for centuries. Lindqvist’s research has found evidence of a gene exchange between polar bears and brown bears as far back as 150,000 years ago, suggesting the species have come into contact during previous, natural changes in the climate. Scientists are also studying potential hybridization between Arctic foxes, a cold-acclimated northern species, and the red fox.

But the big thing Lindqvist and other scientists are watching for is just how much this current period of human-caused warming – by far the most rapid in tens of millions of years – will put species into contact with each other.

Hybridization may be a good thing in some cases, helping species adapt to a rapidly warming planet, said Daniel Rubinoff, an entomology professor and director of the University of Hawaii Insect Museum.

For others it could spell the end of the line.

“It’s not to say that some hybridization isn’t natural, or even something that’s been occurring forever,” Rubinoff told CNN. “But the problem is that it’s too much too fast. This isn’t good, and climate change is not going to overall help our planet’s biodiversity or ecosystems.”

An unusual fish

The hybrid first showed up in Vermont lakes around 2009 or 2010, state fisheries biologist Shawn Good estimates.

The long, tubular fish is the unintentional offspring of two different species; it has a combination of the green-yellow patterns of a northern pike and black scales that resemble chains – a signature of a chain pickerel.

Good realized the species had been unwittingly mating with each other, and the culprit behind the genetic mix-up was Vermont’s warming winters and springs.

Northern pike start to spawn in early April when water temperature is hovering in the high 30s and low 40s, while the chain pickerel typically show up a few weeks later when the water warms up. But spring warmth is coming earlier in the marshy areas where both species spread their eggs and milt, leading to accidental hybridization.

The hybrid fish have become common in Vermont lakes and are regularly caught by anglers and state scientists. Good estimates he sees dozens of them a year.

Another troublesome sign for the fish: the hybrids are sterile and can’t reproduce themselves. Good said autopsies that have been performed on the fish show their reproductive organs aren’t mature.

That isn’t spelling danger just yet for hybrids’ unintentional parents. Enough northern pike and chain pickerel are still spawning with each other to keep those fish lines strong; currently the fish hybridization happens at the tail end of the pike spawning season and the very beginning of the pickerel’s mating.

But Good is aware that could change.

“There’s a real possibility these types of hybrids do increase in abundance and numbers as our spring temperature regimes change over time,” Good said. “If it gets warmer faster, these fish that are typically separated by a few weeks and a few degrees may find themselves spawning in a much tighter period of time.”

In many of these cases, Rubinoff said, cold-adapted animals like polar bears, arctic foxes and northern pike are seeing more warm-weather animals encroaching on their territory.

“In these cases, I think what may happen is there’s going to be a loser,” Rubinoff said. “In most of these cases, I’m guessing it’s going to be the species that was cold adapted.”

Losing their habitat

Not all scientists agree that climate change is speeding up species hybridization. Some argue the other major factor – both contributing to hybridization and species extinction – is habitat loss as human development encroaches on the natural world.

“I will push back against the idea that hybridization between animals or plants or fungi or whatever right now may be increasing in frequency due to climate change,” said Michael Arnold, a genetics professor at the University of Georgia. “Climate change will cause certain habitats to be lost. But those habitats can be regained if we don’t build cities on top of them.”

Arnold, like other scientists, believes the current extinction rate is exponentially larger than past ones. Habitat loss is a primary driver, but climate change is ramping up the pace, Rubinoff argued.

“The idea is this has always happened. It’s the pace that’s faster,” Rubinoff said. “It’s like when people say extinction has always happened. That’s true, but it’s never been this fast. That’s what’s disintegrating ecosystems; they can handle some change, but you can’t just ramp it up.”

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